Russian opposition leaders released a report on Thursday highlighting claims of $25 billion being stolen during preparations for the Sochi 2014 Winter Olympics.

"The main conclusion from the first chapter of our report is that, in preparing for the Olympics, $25-30 billion were stolen," Russian opposition leader Boris Nemtsov said during a press conference in Moscow.

The report was written by Nemtsov and Leonid Martynyuk and is titled An Independent Expert Report on the Winter Olympics in the Subtropics.

"The expenses for the Winter Olympics in Sochi turned out to be more than all expenses for all the sports structures from all the Winter Olympics put together," Nemtsov added.

The report also pointed out that many of the more expensive structures were commissioned without competition or public tenders.

Nemtsov said he would request Russia's Investigative Committee to launch a probe into the matter.

Russia has said the cost of hosting the Games could reach $50 billion, nearly five times more than the original estimation.